Injection apparatus

An injection apparatus comprising:

• an injection piston connected to a screw disposed in a heating barrel to be movable and rotatable along an axial direction of the heating barrel and configured to drive the screw along the axial direction;
• an injection hydraulic cylinder configured to drive the injection piston in the axial direction by pressure of hydraulic oil, and configured to be partitioned into a first chamber to which hydraulic oil pressured in order to drive the injection piston is supplied and a second chamber from which hydraulic oil is discharged, the first chamber driving the injection piston in the axial direction by hydraulic pressure;
• a first oil discharge port configured to discharge the hydraulic oil from the second chamber, the first oil discharge port being disposed in the injection hydraulic cylinder to be blocked by a piston part when the piston part of the injection piston advances to a pressure-holding switching position;
• and
• a second oil discharge port disposed in the injection hydraulic cylinder to discharge the hydraulic oil from the second chamber regardless of the position of the injection piston, wherein
• the injection piston comprises:
• a first member disposed on a side of the first chamber and extending in the axial direction;
• and
• a second member disposed on a side of the second chamber, connected to the first member in the piston part, and extending in the axial direction,
• a joint between the first member and the second member is disposed in the piston part at a position separated from an end of the piston part on a side of the second member by a predetermined distance in the axial direction.